I'm a Kindle author, and many of my books have done very well. A recent book of mine sold over 2000 copies per month, but as was expected, demand tapered off to only about 900 copies last month (the 2000 copy months were October and November).
In response to this I looked at every review of my book (and there were many), but specifically at the most negative and addressed their concerns. There are always some reviewers that you just can't please, or that will not give reasons for their reviews, but spending three hours last weekend going through the reviews I had received and updating my book to reflect those concerns has dramatically increased my sales rankings.
My book is now back at around #2500 on Amazon's sales rankings, and all the reviews since the updates have been positive.
My issue was I didn't want to look at the negative reviews, and I just wanted to ignore them, but by addressing them I've increased my income from my books by 33%, hundreds of dollars a month.
What are your tips for easily increasing your Kindle sales?
Hope this helps,